110 



HISTORY OF THE VEGETABLE KINGDOM. 



Bi)ecie3 of seeds require different proportions of 

 oxygen for their germination. Tlio quantity of 

 this gas consumed by the bean and lettuce, be- 

 fore the commencement of germination, seemed 

 to be equal, and amounted to an lOOtli part of 

 their weight; wliile the quantity consumed by 

 wheat, barley, and purslain, which seemed also 

 to be equal, was only about 1000th part of 

 tlieir weiglit. Tlie carbon lost at the same time, 

 is only about one-tliird part of these quantities; 

 and the oxygen consumed is in proportion to 

 the weight of the seeds, not in proportion to their 

 size or number. 



But Iluber and Senebicr detail experiments, 

 in which certain seeds are said to liave germin- 

 ated in an atmosphere of pure hydrogen and ni- 

 trogen gases. In these cases, the usual carbonic 

 acid gas being also evolved, as in ordinary 

 germination, the question arises whence tlie 

 oxygen was derived necessary to the formation 

 of the carbonic acid. Senebier accounts for it 

 from the decomposition of tlie water contained 

 in the seed, while Saussurc, doubting this theory, 

 repeated the experiments whicli gave rise to it, 

 and found that no seeds would germinate in an 

 atmosphere of pure hydrogen, or nitrogen; and 

 that the seeming exceptions may be accounted 

 for from the action of the uncombined oxygen, 

 contained in the water in which the seed had 

 been placed, or previously steeped. Even after 

 the process of germination has taken place, if 

 tlie young plant be immersed in an atmosphere 

 of eitlier of those gases, vegetation and life will 

 immediately cease. It is true that seeds im- 

 mersed in water, do evolve a portion of carbonic 

 acid, carbonated hydrogen, and nitrogen gases; 

 but these separate from the seed during the pro- 

 cess of fennentation, when this process is passing 

 into that of putrefaction, 



M. Rollo liad observed, that during the pro- 

 cess of germination, many seeds had their mu- 

 cilage converted into sugar; but finding that this 

 process never took place where there was no access 

 of oxygen, and knowing that sugar contains 

 more oxygen than mucilage, he concluded that 

 the accession of oxygen was derived either from 

 the atmosphere, or from tlie decomposition of the 

 water in which the seeds were soaked. He as- 

 certained that it could not be derived from the 

 atmosphere surrounding the plant, as its ele- 

 ments remained the same, and therefore con- 

 cluded, that it was obtained by the decomposi- 

 tion of water. Saussnre supposed that the same 

 facts may be established from the circumstance 

 that the carbon of the seed suffers diminution. 

 But finding that a certain weight of dried seeds, 

 after germination, contained more carbon than 

 the same weight Ijefoi-e this process, he instituted 

 experiments, by which he established that if any 

 seed wliatever is subjected to the germinating 

 process, it actually loses weight, in a proportion 



greater than what might be allowed for its loss 

 of carbon and mucilage during this process. 

 Saussnre attributes this circurastiince to a dimi- 

 nution of the water formerly existing in a fixed 

 state in the seed. A quantity of peas gathered 

 for some years, and dried in a stove, were found 

 to weigh 200 grains. They then underwent the 

 genninating process, in a vessel placed over mer- 

 cury, amid five times their weight of water, 

 and an atmosphere of common air. When ger- 

 mination was completed, 4^ cubic inches of 

 carbonic acid gas were found to have been pro- 

 duced in the receiver, which, according to La- 

 voisier, contains 0.85 parts of a grain of carbon. 

 The water which was now evaporated, left as a 

 residuum, 0.75 parts of a grain of mucilage, and 

 extract; and the seeds which were again dried, 

 evolved during this process, a quantity of car- 

 I'On, in the form of carbonic acid, very nearly 

 equal to the quantity lost in germination. The 

 seeds, therefore, ought to have weighed 197^ 

 grains; but their actual weight wasonly 189 grains. 

 Now, besides the principles already mentioned, 

 they could have lost only water, and this losa 

 amounted to 8| grains. It remained to be 

 proved then, whether the loss ai-ose in the pro- 

 cess of germination, or in drying afterwards. 

 The latter was the case. 



Such are the phenomena, physical or chemical, 

 observable in the germination of the seed. A ir and 

 moisture are absorbed from the soil oratmosphere; 

 their agency is immediately exerted on the far- 

 ina of the albumen or cotyledons; and a food is 

 thus prepared for the nourishment of the tender 

 embryo, to which it passes through the medium 

 of the vessels of the cotyledons, or, as they have 

 been also denominated, the seminal root. The 

 radicle gives the first indications of life, expand- 

 ing and bursting its integuments, and at length 

 fixing itself in the soil : the plumulet next un- 

 folds its parts, developing the rudiments of leafj 

 branch, and trank; and finally the seminal leaves 

 decay and drop off ; and the embryo has been 

 converted into a plant capable of abstracting 

 immediately from the soil or atmosphere, the 

 nourishment necessary to its future growth. 



CHAP XVIII. 



TUB FOOD OF VEGETABLES. 



Aftf.r the embryo, as we have seen, has been 

 converted into a plant, and after it has exhausted 

 the store of nutritious matter prepared for it by 

 the cotyledons, it then has to seek its future 

 nourishment from the soil by means of its roots, 

 and from the air by its leaves. It remains to 

 be considered then, what are the substances 

 which plants derive from the earth and air. 



